Rainbow Electronics AT86RF211 - Manual (Page 30)

30
AT86RF211
1942C–WIRE–06/02
If the tolerance is too high, the rate value is reached earlier, and the rate value could be
unstable (too big step).
If the tolerance is too low, it could be difficult to catch up the DATA and the function
could get lost.
Notice that maximum acceptable distance between two data transitions depends on the
precision of DATARATE versus transmitter actual data rate.
Synchronization mechanism is explained with the chronogram hereafter. The synchroni-
zation is done for the first bit. In worst case conditions, when data and clock arrive at the
same time, it begins at the second bit. Notice that the DATACLK signal is available as
soon as the DATACLK bit is programmed, whatever the state of DATAMSG pin.
The programmed data rate allows the creation of a basic clock at the programmed DAT-
ARATE frequency at the beginning of the reception. Then, the clock is shifted if
necessary from the tolerance value, depending on the previous DATA transition: the
clock is moved later or sooner, depending on the gap between CLOCK and DATA.
For example:
if DATARATE = 50 kbps, which is equivalent to a duration of 200 x T for 1 bit, with
T = 100 ns = base clock period.
if DATATOL = 2% x DATARATE = 4 x T.
Figure 34. Clock Recovery
• DATARATE Programming
This value must be programmed only when the DATA clock is needed on DATACLK
output pin of the chip.
The DATA rate can be programmed from 1 kbps to 64 kbps with 14 bits of CTRL2
register.
DATARATE is the period of the data rate and can be programmed with a resolution
given by the crystal oscillator period:
• 10.245 MHz oscillator, period = T = 97.6 ns
• 20.945 MHz oscillator, period = T = 95.5 ns
Some datarate values with the 10.245 MHz oscillator given for example:
Tol = 4T
Synchronized values with DATAMSG Expected value Expected value
200T
DATAMSG
DATACLK
Tol = 4T
DATARATE[13:0] Rate Period
(160)
10
64 kbps 1 bit ~ 160 x T
(205)
10
50 kbps 1 bit ~ 205 x T
(vv)
10
…… 1 bit ~ vv x T
(534)
10
19.2 kbps 1 bit ~ 534 x T
(1024)
10
10 kbps 1 bit ~ 1024 x T